This invention relates to a softgel formulation containing retinol, and to a softgel formulation containing both retinol and ascorbic acid.
Retinol, along with other retinoids, has enjoyed increasing popularity as an active ingredient in skin care compositions, especially for acne, photoaging, and sun damage. However, more so than other retinoids, retinol tends to decompose on exposure to light, heat, and oxygen. The problem of decomposition has been addressed to some extent by formulating retinol with antioxidants and chelating agents, and storing it in opaque or colored containers, and several patents and published applications, for example, PCT International Application Publication No. WO 93/00085 and European Patent Application Publication Nos. 0 440 398 and 0 596 106, all to Johnson & Johnson, describe water-in-oil emulsions containing retinol, which are asserted to be stable. European Patent Application Publication No. 0 781 551, to Advanced Polymer Systems, discloses an oil-in-water emulsion containing retinol, in which the retinol is entrapped within the pores of solid porous polymeric microparticles. The disclosures of these and other documents referred to in this application are incorporated herein by reference.
Softgel (soft gelatin capsule) formulations have recently become of greater interest in the formulation of products for topical application to the skin, because the softgels provide an attractive single use method for dispensing the product. Typically, these softgels contain 0.1 mL to 2 mL of a fill material, and have a "twist-off" or other removable feature at one end for dispensing the fill material. Such softgels can be prepared by methods well known for the preparation of softgels for oral dosage formulations, i.e. by encapsulating the fill material between two sheets of gelatin as it passes between a pair of die rolls having surface cavities shaped to form the desired shape of the resulting softgel.
However, it is well known in the art that unmodified softgels are incompatible with water, and that typical emulsions, whether water-in-oil or oil-in-water, will degrade the gelatin shell of a softgel.
U.S. Pat. No. 5,587,149 (Punto et al.) discloses a softgel formulation for water-soluble active ingredients, such as ascorbic acid (vitamin C), where the fill material comprises an emulsion of which a first phase includes polyethylene glycol (into which the water-soluble active ingredient is dissolved) and the second phase includes a silicone fluid.
It would be of value to have a softgel formulation containing retinol, and a formulation containing retinol and ascorbic acid.